Pump Apparatus

ABSTRACT

A pump apparatus which is expected to realize satisfactory work efficiency of an assembly operation, reduction of noise and suppression of rust comprises: two pump units ( 22  and  23 ); a valve unit ( 24 ) provided between the pump units ( 22  and  23 ); and a fastening means ( 36 ) for fastening the pump units ( 22  and  23 ) to each other such that the valve unit ( 24 ) is able to be held by the pump units ( 22  and  23 ) therebetween.

TECHNICAL FIELD

The present invention relates to a pump apparatus.

BACKGROUND ART

FIG. 14 is a perspective view showing a pump apparatus 1 of a prior art.FIG. 15 is a front view showing the pump apparatus 1. FIG. 16 is a sideview showing the pump apparatus 1. The pump apparatus 1 of FIGS. 14 to16 is shown in, for example, “Hydraulics and Pneumatics October ExtraIssue” (Japan Industrial Publishing Co., Ltd, published on Oct. 5,2000), Vol. 39, 12th. The pump apparatus 1 is a combined pump apparatuscalled, for example, a tandem pump in which two swash plate type pistonpumps are arranged axially. The pump apparatus 1 includes two pump units2 and 3 and a valve unit 4. The pump units 2 and 3 include pump casings5 and 6, respectively. In each of the pump casings 5 and 6, a cylinderblock, a piston, a swash plate, etc. are accommodated. The valve unit 4includes a valve casing 7. In the valve casing 7, two valve plates areaccommodated, which are slidable relative to the cylinder blocks of thepump units 2 and 3, respectively.

The pump unit 2 and the valve unit 4 are fastened to each other by aplurality of, for example, four, fastening bolts 10. Similarly, the pumpunit 3 and the valve unit 4 are fastened to each other by four fasteningbolts 10. Each fastening bolt 10 is threadedly engaged with the valveunit 4 in a state in which a head portion of the fastening bolt 10engages with a flange portion of an end portion on one side of each ofthe pump units 2 and 3, the side being opposite a side facing the valveunit 4. An intermediate portion of each fastening bolt 10 is exposedoutside the pump casing 5 or 6.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

In the pump apparatus 1 of the prior art, the axially intermediateportion of the fastening bolt 10 is exposed outside the pump casing 5 or6, so that noise is emitted when the fastening bolt 10 resonates andoscillates at a radio frequency with respect to an n-th frequencycomponent of a fundamental frequency of each of the pump units 2 or 3.Further, since the pump casing 5 or 6 is externally partially covered bythe fastening bolt 10, such covered portion may be paintedinsufficiently and therefore rust.

Since the pump units 2 and 3 are separately fastened to the valve unit 4by the separate fastening bolts 10, the number of the fastening bolts 10to be used becomes large, specifically, eight. Therefore, the number ofprocessed portions of the pump units 2 and 3 and the valve unit 4, suchas screw holes used for fastening by the fastening bolts 10, becomeslarge, and the productivity of components deteriorates. In addition, thenumber of steps of fastening the pump units 2 and 3 and the valve unit 4by the fastening bolts 10 becomes large, so that the work efficiency ofan assembly operation is reduced.

An object of the present invention is to provide a pump apparatus whichrealizes satisfactory productivity of components and satisfactory workefficiency of the assembly operation.

Another object of the present invention is to provide a pump apparatuswhich can reduce the noise and prevent the generation of the rust.

Means for Solving the Problems

The present invention provides a pump apparatus comprising: two pumpunits; a valve unit provided between the pump units; and a fasteningmeans for fastening the pump units to each other such that the valveunit is able to be held by the pump units therebetween.

In accordance with the present invention, by causing the pump units tobe fastened to each other by the fastening means, the valve unitprovided between the pump units is held by the pump units therebetween.Thus, the number of the fastening means can be reduced compared to theconstruction in which the pump units are separately fastened to thevalve unit. Therefore, it is possible to reduce the number of processedportions of the pump units and the valve unit, the processed portionsbeing used to fasten the pump units and the valve unit by the fasteningmeans, and the productivity of components of the pump apparatus can bemade satisfactory. In addition, the number of steps of fastening thepump units and the valve unit can be reduced, so that the workefficiency of the assembly operation of the pump apparatus can be madehigh.

Moreover, the fastening means may be provided so as to be insertedthrough the valve unit. In accordance with this construction, thefastening means is externally covered by the valve unit, so that thefastening means is not exposed outside. Therefore, even if the fasteningmeans resonates and oscillates at a radio frequency with respect to then-th frequency component of the fundamental frequency of the pump unit,the emitting of the noise generated due to the oscillation is prevented.On this account, the noise of the pump apparatus can be reduced.Moreover, since the fastening means does not cover the pump units or thevalve unit, a painting operation of the pump apparatus is easy, and theoccurrence of a painting failure can be prevented. Therefore, thegeneration of the rust caused by the painting failure can be prevented.

Moreover, the pump apparatus may further comprise a positioning meansfor positioning the pump units and the valve unit.

In accordance with this construction, even in a case where the valveunit is held by the pump units therebetween, the pump units and thevalve unit are positioned by the positioning means. With this, the pumpapparatus can be assembled easily without causing problems includingmalfunctions. The positioning means may be comprised of: a positioningprojection which projects from a first end surface of the pump unit anda first end surface of the valve unit; and an opening which is formed ona second end surface and in which the positioning projection fits.

Effects of the Invention

In accordance with the present invention, the number of the fasteningmeans for fastening the pump units and the valve unit can be reduced.Therefore, since the number of processed portions of the pump units andthe valve unit and the number of steps of the assembly operation can bereduced, the productivity of components of the pump apparatus and thework efficiency of the assembly operation can be made high.

Moreover, in accordance with the present invention, the fastening meansis not exposed outside. Therefore, even if the fastening meansoscillates at a radio frequency, the noise generated due to theoscillation is not emitted. Thus, the noise of the pump apparatus can bereduced. In addition, since the fastening means does not disturb thepainting operation of the pump apparatus, the painting failure isprevented. Therefore, the generation of the rust of the pump apparatusis prevented.

Further, in accordance with the present invention, the pump units andthe valve unit are positioned, so that the pump apparatus can be easilyassembled without causing problems including malfunctions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a pump apparatus of one embodimentof the present invention.

FIG. 2 is a perspective view showing the pump apparatus when viewed froma direction different from that of FIG. 1.

FIG. 3 is a front view schematically showing the pump apparatus.

FIG. 4 is a side view schematically showing the pump apparatus.

FIG. 5 is a cross-sectional view showing a first pump casing.

FIG. 6 is a side view showing the first pump casing when viewed from aright side of FIG. 5.

FIG. 7 is a plane view showing the first pump casing when viewed from anupper side of FIG. 5.

FIG. 8 is a cross-sectional view showing a second pump casing.

FIG. 9 is a side view showing the second pump casing when viewed from aright side of FIG. 8.

FIG. 10 is a plane view showing the second pump casing when viewed froman upper side of FIG. 8.

FIG. 11 is a front view showing a valve unit.

FIG. 12 is a side view showing the valve unit when viewed from a leftside of FIG. 11.

FIG. 13 is a side view showing the valve unit when viewed from a rightside of FIG. 11.

FIG. 14 is a perspective view showing a pump apparatus of a prior art.

FIG. 15 is a front view showing the pump apparatus.

FIG. 16 is a side view showing the pump apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a perspective view showing a pump apparatus 21 of oneembodiment of the present invention. FIG. 2 is a perspective viewshowing the pump apparatus 21 when viewed from a direction differentfrom that of FIG. 1. FIG. 3 is a front view schematically showing thepump apparatus 21. FIG. 4 is a side view schematically showing the pumpapparatus 21. The pump apparatus 21 is a pump apparatus mounted on, forexample, industrial machineries and construction machineries that aremounting targets, and is a combined pump apparatus, called a tandempump, in which two pump portions are combined. The type of two pumps tobe combined is not especially limited, but may be a gear pump. In thepresent embodiment, the pump is, for example, a swash plate type pistonpump. The swash plate type piston pump may be a fixed displacement pump,but is a variable displacement pump in the present embodiment.

The pump apparatus 21 includes first and second pump units 22 and 23 anda valve unit 24, and further includes first and second regulators 25 and26. The pump units 22 and 23 and the valve unit 24 are providedcoaxially, and axes of the pump units 22 and 23 and the valve unit 24constitute an axis L21 of the pump apparatus 21. The pump units 22 and23 and the valve unit 24 are arranged along the axis L21 of the pumpapparatus 21 so as to be connected to each other such that the valveunit 24 is sandwiched by the pump units 22 and 23. The regulators 25 and26 are respectively provided on top of the pump unit 22 and on top ofthe pump unit 23 so as to be respectively connected to the pump units 22and 23.

The pump units 22 and 23 include first and second pump casings 27 and28, respectively. In each of the pump casings 27 and 28, components,such as a cylinder block, a piston, a swash plate, etc., areaccommodated. The valve unit 24 includes a valve casing 30. In the valvecasing 30, two valve plates are accommodated, which are slidablerelative to the cylinder blocks of the pump units 22 and 23,respectively. The valve casing 30 and the valve plates may be formed asa unitary component or as separate components. The regulators 25 and 26include regulator casings 31 and 32, respectively. In each of theregulator casings 31 and 32, a structure for causing the swash plate totilt is accommodated.

The pump apparatus 21 includes a plurality of fastening bolts 36 thatare fastening means. In the present embodiment, four fastening bolts 36are used. The pump units 22 and 23 and the valve unit 24 are fastened toeach other by the fastening bolts 36. The pump units 22 and 24 areprovided so as to be fastened to each other by the fastening bolts 36such that the accommodated cylinder blocks, pistons, swash plates, etc.are substantially symmetrical to each other. Each fastening bolt 36 isprovided to extend substantially in parallel with the axis L21 of thepump apparatus 21. Since the valve unit 24 is provided between the pumpunits 22 and 23, it is held by the pump units 22 and 23 therebetween.Thus, the pump units 22 and 23 and the valve unit 24 are connected toeach other.

End portions of the fastening bolt 36 engage with the pump casings 27and 28, respectively, so that the pump casings 27 and 28 are fastened toeach other. A structure of how each end portion of the fastening bolt 36engages with the pump casing 27 or 28 is realized by, for example, anyone of constructions in which a head portion of the fastening bolt 36engages with the pump casing 27 or 28, in which the fastening bolt 36 isthreadedly engaged with the pump casing 27 or 28, and in which a nutmember which is threadedly engaged with the fastening bolt 36 engageswith the pump casing 27 or 28. The fastening bolt 36 is provided so asto be inserted through the valve unit 24, and an axially intermediateportion between both end portions of the fastening bolt 36 is notexposed outside.

The pump apparatus 21 includes a positioning means. The positioningmeans can position the pump units 22 and 23 and the valve unit 24regarding a direction crossing the axis L21 of the pump apparatus 21 soas to prevent relative displacements of the pump units 22 and 23 and thevalve unit 24. The positioning means is not an essential component, andfor example, the relative displacements may be prevented by frictionalforces acting between the pump units 22 and 23 and the valve casing 24.In the present embodiment, the positioning means is included. Thespecific construction of the positioning means is not limited, but maybe any construction as long as the positioning means can position thepump units 22 and 23 and the valve unit 24 so as to prevent thedisplacements.

The pump unit 22 includes a rotational shaft. The rotational shaft isrotatably supported by the first pump casing 27 via a bearing. Thecylinder block is splined to the rotational shaft or connected to therotational shaft by a key, and the rotational shaft and the cylinderblock are integrally rotatable. The cylinder block is provided with aplurality of piston chambers, and pistons fit in the piston chambers soas to be extendable and retractable. The piston contacts, at one endportion thereof projecting from the cylinder block, a supporting surfaceof the swash plate via a shoe so as to be displaced along the supportingsurface. The supporting surface of the swash plate is inclined relativeto a virtual flat surface perpendicular to a rotational axis. The pistoncarries out a reciprocating displacement that is extending andretracting in accordance with the rotation of the cylinder block.

A first valve plate that is one of the valve plates provided in thevalve unit 24 is provided with an inlet port which is connected to, forexample, a tank that is an oil source storing hydraulic oil that ishydraulic fluid, and an outlet port which is connected to, for example,an actuator to which the hydraulic oil is supplied. The valve plate isconstructed such that the piston chamber in which the piston in anextending stroke fits is connected to the inlet port and the pistonchamber in which the piston in a retracting stroke fits is connected tothe outlet port. Therefore, when power is transferred from a power unitto the rotational shaft to rotate the cylinder block, the hydraulic oilis suctioned from the tank by the reciprocating displacement of thepiston so as to be supplied to the actuator.

The first regulator 25 can cause the swash plate to tilt to change atilt angle of the supporting surface of the swash plate by controlling aservo mechanism provided in the first pump unit 22. With this, a pumpcapacity can be changed. Thus, the first pump unit 22, the firstregulator 25 connected to the first pump unit 22, and some componentsincluding the first valve plate of the valve unit 24 constitute a firstpump portion.

The second pump unit 23 has substantially the same construction as thefirst pump unit 22, and the second regulator 26 has substantially thesame construction as the first regulator 25. The second pump unit 23,the second regulator 26 connected to the second pump unit 23 and somecomponents including a second valve plate that is another valve plate ofthe valve unit 24 constitute a second pump portion. This second pumpportion has substantially the same construction as the first pumpportion constructed of the first pump unit 22, the regulator 25connected to the first pump unit 22 and some components including thefirst valve plate of the valve unit 24.

These pump portions have the same construction as each other except thatonly the first pump casing 27 of the first pump unit 22 is provided witha fixing flange portion 58 to be attached to a body of the mountingtarget, and the constructions of respective rotational shafts aredifferent from each other. The rotational shaft of the first pumpportion including the first pump unit 22 projects from the first pumpcasing 27, and power is transferred from a power unit to this rotationalshaft. The rotational shaft of the second pump portion including thesecond pump unit 23 is connected, in the valve unit, to the rotationalshaft of the first pump portion including the first pump unit 22.Therefore, these two pump portions operate in association with eachother.

FIG. 5 is a cross-sectional view showing the first pump casing 27. FIG.6 is a side view showing the first pump casing 27 when viewed from aright side of FIG. 5. FIG. 7 is a plane view showing the first pumpcasing 27 when viewed from an upper side of FIG. 5. The first pumpcasing 27 has an accommodating space 44. In the accommodating space 44,components including the rotational shaft, the cylinder block, thepistons and the swash plate are accommodated. The accommodating space 44axially penetrates through the first pump casing 27. The accommodatingspace 44 opens by an opening 48 at a first side surface portion 45 thatis a first axial end portion of the first pump casing 27, and opens byan opening 49 at a second side surface portion 46 that is a second axialend portion of the first pump casing 27. In addition, the accommodatingspace 44 opens by an opening 50 at a flat surface portion 47 that is anupper end portion of the first pump casing 27.

The first pump casing 27 includes on the second side surface portion 46a plurality of connecting flange portions 55 which are arranged so as tobe spaced apart from each other in a circumferential direction andproject radially outwardly. In the present embodiment, the first pumpcasing 27 includes four connecting flange portions 55. Each connectingflange portion 55 has a fastening screw hole 56 in which an internalthread is formed. An axis L56 of each screw hole 56 is in parallel withan axis L27 of the first pump casing 27. The axis L27 of the first pumpcasing 27 is identical with the axis L21 of the pump apparatus 21.

Moreover, the first pump casing 27 includes on the first side surfaceportion 45 a plurality of, for example, two, mounting and fixing flangeportions 58 which project radially outwardly. Each mounting and fixingflange portion 58 has a fixing insertion through hole 59.

FIG. 8 is a cross-sectional view showing the second pump casing 28. FIG.9 is a side view showing the second pump casing 28 when viewed from aright side of FIG. 8. FIG. 10 is a plane view showing the second pumpcasing 28 when viewed from an upper side of FIG. 8. The second pumpcasing 28 has an accommodating space 64. In the accommodating space 64,components including the rotational shaft, the cylinder block, thepistons and the swash plate are accommodated. The accommodating space 64axially penetrates through the second pump casing 28. The accommodatingspace 64 opens by an opening 68 at a first side surface portion 65 thatis a first axial end portion of the second pump casing 28, and opens byan opening 69 at a second side surface portion 66 that is a second axialend portion of the second pump casing 28. In addition, the accommodatingspace 64 opens by an opening 70 at a flat surface portion 67 that is anupper end portion of the second pump casing 28.

The second pump casing 28 includes on the second side surface portion 66a plurality of connecting flange portions 75 which are arranged so as tobe spaced apart from each other in a circumferential direction andproject radially outwardly. In the present embodiment, the second pumpcasing 28 includes four connecting flange portions 75. Each connectingflange portion 75 has an engaging hole 76. Each engaging hole 76 iscomprised of a main hole portion 76 a which is formed on the second sidesurface portion 66 side in an axial direction of the second pump casing28 so as to have a small diameter and a concave portion 76 b which isformed on the first side surface portion 65 side in the axial directionof the second pump casing 28 so as to have a large diameter. There is astep between an inner peripheral surface of the main hole portion 76 aand an inner peripheral surface of the concave portion 76 b. An axis L76of each engaging hole 76 is in parallel with an axis L28 of the secondpump casing 28. The axis L28 of the second pump casing 28 is identicalwith the axis L21 of the pump apparatus 21.

FIG. 11 is a front view showing the valve unit 24. FIG. 12 is a sideview showing the valve unit 24 when viewed from a left side of FIG. 11.FIG. 13 is a side view showing the valve unit 24 when viewed from aright side of FIG. 11. The valve casing 30 of the valve unit 24accommodates a valve block 80. The valve casing 30 and the valve block80 are formed integrally. Two valve plates 201 and 202 are fixed to thevalve block 80 so as not to be rotatable. In the valve casing 30, anaccommodating space 81 accommodating the valve block 80 opens at anaxial end portion 84 by an opening 86 and at an axial end portion 85 byan opening 87.

The valve casing 30 of the valve unit 24 has a plurality of, in thepresent embodiment, four, insertion through holes 90. The insertionthrough holes 90 are formed in an outer peripheral portion of the valveunit 24 so as to be spaced apart from each other in a circumferentialdirection. The insertion through hole 90 is a cylindrical hole. An axisL90 of each insertion through hole 90 is in parallel with an axis L24 ofthe valve unit 24. The axis L24 of the valve unit 24 is identical withthe axis L21 of the pump apparatus 21.

Referring to FIGS. 1 to 13, the pump units 22 and 23 and the valve unit24 are arranged such that the axes of the pump casings 27 and 28 and theaxis L24 of the valve unit 24 coincide with each other, and the valveunit 24 is sandwiched by the pump units 22 and 23. Which surface of thevalve unit 24 face which of the pump units 22 and 23 is not especiallylimited, but can be suitably selected depending on the construction ofthe mounting target and the rotational direction of the pump apparatus21. Although it is just one example, in the example shown in FIGS. 1 to13, the first pump unit 22 is provided such that the second side surfaceportion 46 faces the first axial end portion 84 of the valve unit 24,and the second pump unit 23 is provided such that the second sidesurface portion 66 faces the second axial end portion 85 of the valveunit 24. Further, the pump units 22 and 23 and the valve unit 24 arearranged such that respective axes L56 of the screw holes 56, theircorresponding axes L76 of the engaging holes 76 and their correspondingaxes L90 of the insertion through holes 90 coincide with each other soas to be placed coaxially. Thus, four holes are formed, each of which isformed by axially arranging and connecting the screw hole 56, theinsertion through hole 90 and the engaging hole 76 in this order.

The fastening bolt 36 has at its first axial end portion, a screwportion 36 a on which an external thread is formed and at second axialend portion, a head portion 36 b which projects radially outwardly. Thefastening bolts 36 are respectively inserted into four holes, eachformed by the screw hole 56, the insertion through hole 90 and theengaging hole 76, from the engaging hole 76 through the insertionthrough hole 90 to the screw hole 56 such that the screw portion 36 a islocated on the first pump unit 22 side and the head portion 36 b islocated on the second pump unit 23 side. The fastening bolts 36 areprovided such that: each head portion 36 b fits in the concave portion76 b of the engaging hole 76 so as to contact a step surface of aboundary between the main hole portion 76 a and the concave portion 76 bin a state where the displacement of the fastening bolt 36 relative tothe second pump casing 28 in a direction perpendicular to the axis ofthe fastening bolt 36 is prevented, thus engaging with the second pumpcasing 28; and each screw portion 36 a is threaded into the screw hole56 so as to be fastened to the first pump casing 27.

Thus, the end portions 36 a and 36 b of the fastening bolt 36respectively engage with the pump casings 27 and 28, so that the pumpcasings 27 and 28 are fastened to each other. The valve unit 24 isprovided between the pump units 22 and 23 so as to be sandwiched by thepump casings 27 and 28. Thus, the valve unit 24 is held by the pumpunits 22 and 23 therebetween. To be specific, the valve casing 30 isheld by the pump casings 27 and 28 therebetween. Therefore, the pumpunits 22 and 23 and the valve unit 24 are connected to each other suchthat the valve unit 24 is sandwiched by the pump units 22 and 23, andthe pump units 22 and 23 are fastened to each other.

In the present embodiment, as a positioning means for positioning thepump units 22 and 23 and the valve unit 24, projecting portions 33 and34 and positioning pins 95 are provided.

The projecting portions 33 and 34, called pilot portions, arerespectively formed on the axial end portions 84 and 85 of the valvecasing 30 so as to project axially. Moreover, the projecting portions 33are formed in an annular shape extending in a circumferential directionso as to respectively surround the openings 86 and 87 of the axial endportions 84 and 85 of the valve casing 30. Further, the projectingportions 33 and 34 are formed coaxially with the axis L24 of the valveunit 24. In a state where the pump units 22 and 23 and the valve unit 24are arranged, the projecting portion 33 and 34 respectively fit in theopening 49 and 69 of the second side surface portions 46 and 66 of thepump casings 27 and 28 so as to be respectively supported from radiallyoutwardly by inner peripheral surface portions 205 and 206 whichrespectively surround the openings 49 and 69. Each of the openings 49and 69 of the second side surface portions 46 and 66 of the pump casings27 and 28 has a circular shape so as to be formed coaxially with theaxes L27 and L28 of the pump casings 27 and 28. Therefore, by causingthe projecting portions 33 and 34 to respectively fit in the openings 49and 69 of the second side surface portions 46 and 66 of the pump casings27 and 28, the pump casings 27 and 28 and the valve casing 24 arepositioned so as to be coaxial with each other.

The second side surface portion 46 of the pump casing 27 and the secondside surface portion 66 of the pump casing 28 have bottomed fittingholes 100 and 101, respectively. The valve casing 30 of the valve block24 has a bottomed fitting hole 102 at the axial end portion 84 and abottomed fitting hole 103 at the axial end portion 85. As describedabove, in a state where the pump units 22 and 23 and the valve unit 24are placed coaxially, and the screw holes 56, their correspondinginsertion through holes 90 and their corresponding engaging holes 76 areplaced coaxially, the fitting hole 100 of the first pump casing and thefitting hole 102 of the first axial end portion of the valve casing 30are placed coaxially, and the fitting hole 101 of the second pump casingand the fitting hole 103 of the second axial end portion of the valvecasing 30 are placed coaxially.

One of the positioning pins 95 fits in the fitting hole 100 of the firstpump casing and the fitting hole 102 of the first axial end portion ofthe valve casing 30, and another positioning pin 95 fits in the fittinghole 101 of the second pump casing and the fitting hole 103 of thesecond axial end portion of the valve casing 30. With this, the valveunit 24 can be positioned relative to the pump units 22 and 23 whilepreventing the displacement of the valve unit 24 in a circumferentialdirection around the axis L21 of the pump apparatus 21.

As in the present invention, in the construction in which the valve unit24 is held by the pump units 22 and 23 therebetween fastened to eachother, so as to be connected to the pump units 22 and 23, the pump units22 and 23 are positioned regarding a direction crossing the axis L21 ofthe pump apparatus 21 by four fastening bolts 36 provided in acircumferential direction. The valve unit 24 is positioned relative tothe pump units 22 and 23 by the positioning means. Thus, the positioningis accomplished easily and highly precisely by using the projectingportions 33 and 34 and the positioning pins 95.

The fitting holes 102 and 103 of the valve unit 24 are placed atpositions shifted from each other in a direction perpendicular to theaxis L24 of the valve unit 24. In other words, the fitting holes 102 and103 of the valve unit 24 are formed non-coaxially each other. In thepresent embodiment, the fitting hole 102 of the first axial end portion84 side is formed at a position close to a bottom surface portion andrear surface portion of the valve unit 24, and the fitting hole 103 ofthe second axial end portion 85 side is formed at a position close tothe bottom surface portion and front surface portion of the valve unit24. Therefore, the positioning pins 95 are provided so as to be shiftedfrom each other in a direction perpendicular to the axis L21 of the pumpapparatus 21, that is, the positioning pins 95 are providednon-coaxially.

The pump apparatus 21 is fixed to the body of the mounting target by themounting and fixing flange portion 58 of the first pump unit 22. In thisstate, the pump apparatus 21 is connected to the power unit provided inthe mounting target, so as to be driven to supply the hydraulic oil tothe actuator of the mounting target.

In accordance with the present embodiment, by causing the pump units 22and 23 to be fastened to each other by the fastening bolts 36, the valveunit 24 provided between the pump units 22 and 23 is held by the pumpunits 22 and 23 therebetween. Thus, the number of the fastening bolts 36can be reduced compared to the construction in which the pump units 22and 23 are separately fastened to the valve unit 24. Therefore, it ispossible to reduce the number of processed portions of the pump units 22and 23 and the valve unit 24, the processed portions being used tofasten the pump units 22 and 23 and the valve unit 24 by the fasteningbolts 36. Specifically, it is possible to reduce the number of portionswhere the screw hole 56, the engaging hole 76 and the insertion throughhole 90 are formed. Therefore, the productivity of components of thepump apparatus 21 can be made satisfactory. In addition, the number ofsteps of fastening the pump units 22 and 23 and the valve unit 24 can bereduced, so that the work efficiency of the assembly operation of thepump apparatus 21 can be made high.

Moreover, by causing the fastening bolts 36 to be respectively insertedthrough the insertion through holes 90 of the valve unit 24, thefastening bolts 36 are externally covered by the valve unit 24, so thatat least the axially intermediate portion of the fastening bolt 36 isnot exposed outside. Therefore, even if the fastening bolt 36 resonatesand oscillates at a radio frequency with respect to the n-th frequencycomponent of the fundamental frequency of the pump units 22 and 23, theemitting of the noise generated due to the oscillation is prevented. Onthis account, the noise of the pump apparatus 21 can be reduced.Moreover, since the fastening bolt 36 does not externally cover the pumpunit 22 or 23 or the valve unit 24, the painting operation of the pumpapparatus 21 including the pump units 22 and 23 and the valve unit 24 iseasy, and the occurrence of the painting failure can be prevented.Therefore, the generation of the rust caused by the painting failure canbe prevented.

Moreover, even in a case where the valve unit 24 is held by the pumpunits 22 and 23 therebetween, the pump units 22 and 23 and the valveunit 24 are positioned by the positioning means. With this, the pumpapparatus 21 can be assembled easily without causing problems includingmalfunctions in such a manner that the pump units 22 and 23 and thevalve unit 24 are placed surely coaxially.

The above-described embodiment is just an illustration of the presentinvention, and the constructions may be modified.

INDUSTRIAL APPLICABILITY

In accordance with the present invention, the number of the fasteningmeans for fastening the pump units and the valve unit can be reduced,and the number of processed portions of the pump units and the valveunit and the number of steps of the assembly operation can be reduced.Therefore, the present invention is useful for so-called tandem pumps.

1. A pump apparatus comprising: two pump units; a valve unit providedbetween the pump units; and a fastening means for fastening the pumpunits to each other such that the valve unit is able to be held by thepump units therebetween.
 2. The pump apparatus according to claim 1,wherein the fastening means is provided so as to be inserted through thevalve unit.
 3. The pump apparatus according to claim 1, furthercomprising a positioning means for positioning the pump units and thevalve unit.
 4. The pump apparatus according to claim 3, wherein thepositioning means is comprised of: a positioning projection whichprojects from a first end surface of the pump unit and a first endsurface of the valve unit; and an opening which is formed on a secondend surface and in which the positioning projection fits.